The biological effects and pharmacokinetics of synthetic polymers linked to antitumor agents are being investigated. Initial trials are being conducted with divinylethermaleic anhydride copolymer covalently bound to methotrexate. Activated sulfhydryl derivatives of cyclophosphamide and their polymer linked derivatives are also being investigated. The purpose is to determine whether pharmacokinetic behavior of active drug forms can be related to cytotoxic activity. DNA crosslinking in vitro is being related to antitumor activity in vivo.